The present technology relates to a memory control device, a non-volatile memory, and a memory control method. Specifically, the present technology relates to a memory control device, a non-volatile memory, and a memory control method which are used to verify whether or not rewrite is successful.
In recent information processing systems, there are cases in which non-volatile memories (NVMs) are used as auxiliary storage devices or storages. The non-volatile memories are roughly divided into flash memories supporting data access using a large size as a unit and non-volatile random access memories (NVRAMs) capable of performing high-speed random access in small units. Here, as a representative example of a flash memory, there is a NAND flash memory.
Meanwhile, as an example of a non-volatile random access memory, there are a resistive RAM (ReRAM) and the like. In addition, a phase-change RAM (PCRAM), a magnetoresistive RAM (MRAM), and the like are known. Particularly, ReRAMs are capable of performing rewrite using a pulse having a short duration on the order of several nanoseconds (ns). For this reason, ReRAMs are attracting public attention as a non-volatile memory capable of performing a high-speed operation.
In a rewrite process of such a non-volatile memory, generally, a write process of rewriting data in a memory cell is executed, and then a verifying process of verifying whether or not an error has occurred at the time of rewrite is executed. Then, when an error has occurred, a retry process of performing rewrite again is executed. In the write process and the retry process, as the number of bits to be rewritten at the same time increases, an electric current necessary for rewrite increases. For example, in NOR (negative OR) flash memories, a rewrite current per bit is about 100 microamperes (μA). For this reason, when 8 bits are rewritten at the same time, an electric current of about 800 μA is necessary. Further, execution times of the write process and the retry process correspond to the number of bits to be written at the same time. For example, when the rewrite speed at the time of rewriting 8 bits at the same time is about 1 microsecond (μs), about 8 seconds are necessary for each of the write process and the retry process of 256 bits.
The amount of an electric current that can be supplied at the time of rewrite is typically restricted by an electric current allowed in a current path and the capacity of a power supply. In this regard, a non-volatile memory in which a current path having a small voltage drop is secured to increase a suppliable current has been proposed as a result of conducting a study on connection of interconnections (for example, see K. Aratani, et al. “A Novel Resistance Memory with High Scalability and Nanosecond Switching,” Technical Digest IEDM 2007, pp 783-786).